It has been well understood for many years that the performance of piston operated internal combustion engines can be substantially improved by varying the valve lift and/or timing in accordance with engine speed and power. While there is no simple mechanical means for adjusting valve cam profiles, it has been recognized that valve lift variation can be achieved, by varying the level and timing of the valve lifter. The importance of varying valve timing, lift, dwell and overlap to meet different operating conditions has long been recognized. Cams profiled for smooth engine operation at low and moderate speeds do not provide efficiency at high speeds. Conversely, cams profiled for high speeds, power and acceleration do not perform efficiently at low speeds, and tend to run rough, provide poor fuel economy, and create greater air pollution. Numerous mechanisms have been developed to provide variable valve timing and lift in diesel and gasoline engines. Typical prior art devices have employed mechanical, hydraulic or solenoid activated mechanisms.
A first type of device operates by effectuating small changes in the over-all length of the lifter. A second type employs a two position system, i.e. a low position (minimum unit extension), and a high position (maximum unit extension). A third type of prior art valve lift device continuously alters valve lifter position, while a fourth type operates by completely deactivating the associated valve. In the Cadillac Modular Displacement System, for example, selected valves are deactivated/activated by shifting rocker arm pivot points by an electric solenoid to remove a selected cylinder completely from operation. Numerous patents for "split engine" operation such as Springer U.S. Pat. No. 4,284,042, Brown Pat. No. 3,964,455, Mueller U.S. Pat. No. 4,151,817 provide means for disabling the valves of selected cylinders. Patents providing selective operation of multi-lobe cams include Wagner U.S. Pat. No. 3,277,874 and Hausknecht U.S. Pat. No. 4,134,371. Additional hydraulic valve deactivation mechanisms are disclosed in U.S. Pat. Nos. 4,442,806 and 4,515,121.
Each of these conventional methods of controlling valve lift, timing and deactivation is complex and expensive. Each requires hydraulic or solenoid activated control systems which are often difficult to position, control, replace and repair. It would be desireable to have a simple valve controller wholly integral to the valve lift mechanism which could control valve lift and timing.
It has been recognized for several decades that certain fluids respond to the influence of an electric potential by evidencing a rapid and pronounced increase in viscosity and an increased resistance to shear. Such electro-rheological or electroviscous fluids comprise slurries of finely divided hydrophilic solids in hydrophobic liquids. In the absence of an electric field, these fluids behave in a Newtonian fashion, but when an electric field is applied, the fluids become proportionately more viscous as the potential of the electric field increases. In strong electric fields, these fluids can thicken into a solid. The electro-rheological phenomenon reverses when the electric potential is removed, and the material returns to its fluid state. Electro-rheological fluids change their characteristics very rapidly when electric fields are applied or released, with typical response times being on the order of one millisecond. The ability of electro-rheological fluids to respond rapidly to electrical signals makes them well suited as elements in mechanical devices. Patents directed to compositions of electro-rheological fluids include U.S. Pat. Nos. 3,367,872; 3,047,507 and 4,033,892. Electro-rheological fluids have been extensively used in clutches as disclosed, for example, U.S. Pat. Nos. 4,444,298 and 4,493,615, and more recently in shock absorbers and hydraulic applications.
Until recently, the practical application of electro-rheological fluids was limited to low temperature environments due to the previously required presence of water in the electro-rheological fluid. In a high temperature environment, the water in the fluid would vaporize and lead to corrosion. This strictly limited the use of electro-rheological fluids away from high temperature applications on or near gasoline and diesel powered automobile and truck engines and the like. Recently, the temperature problem has been minimized with advances in electro-rheological fluid technology such as those disclosed in U.S. Pat. Nos. 4,744,914 and 4,772,407. Electro-rheological devices, because of their special nature offer numerous advantages over mechanical valve control devices incorporating hydraulic, solenoid and cam operated action, such as that utilized in standard valve lifters.
Compression braking has also long been an important feature in heavy trucks, vehicles which operate in mountainous terrain, and racing vehicles. Compression braking is based upon the principle of utilizing engine compression as an energy pump to retard the speed of the pistons and drive shaft. Patents disclosing compression released engine retarders include Price U.S. Pat. No. 4,485,780, Cartledge U.S. Pat. 3,809,033, and Samuel U.S. Pat. 4,393,832. All disclose systems which halt fuel injection during the braking operation and open the exhaust valve to release compression when the piston is close to top of dead center (T.D.C.) position during the compression stroke in a four cycle engine. Each of these devices incorporate the use of complex and expensive hydraulic or solenoid structures (in addition to the standard valve lifters) for lifting the exhaust valve to induce compression braking. The embodiments of the electro-rheological valve control device disclosed herein can, in addition to controlling valve lift and timing, also be applied to create a safer, more reliable and less expensive compression braking mechanism.
In view of the above, it would be desirable to provide a novel valve lift and control mechanism incorporating electro-rheological fluids which can be used in a variety of gasoline and diesel engine applications which are currently performed by complex and expensive solenoid hydraulic and mechanical devices.
It would further be particularly desirable to provide a novel electro-rheological device which can function as a valve controller, lifter and timer and which can replace hydraulic, solenoid and mechanically actuated valve lifters such as those disclosed in U.S. Pat. Nos. 3,865,088 and 4,203,397.
It would further be desirable to provide an electro-rheological device having a novel electrode configuration situated within the device itself which facilitates compactness, control, and facilitates compatibility with the on-board computers and microprocessors found in modern automobiles and trucks.
It would further be desirable to provide a valve lift, timing and control mechanism which can simultaneously function as a compression braking mechanism for diesel engines.
It would further be desirable to provide a replaceable wear strip to alleviate tappet and cam spalling and to provide more convenient maintenance shims.
A principal object of this invention then is to provide an electro-rheological device for varying valve timing, control and lift in response to varying operating conditions such as changes in speed, acceleration, power demand, and temperature, so as to maximize overall efficiency, acceleration, speed and power, and so as to provide smoother operation at all speeds, reduced pollution and increased fuel economy.
Another object of the present invention is to provide a variable valve control unit which can be designed for partial lift in a preset number of positions (i.e. a high lift position or a low lift position), or alternatively to provide infinitely variable control between the high lift and low lift position.
A further object of the invention is to provide an electro-rheological device which permits the rapid deactivation of a selected valve to allow that valve to remain closed while the remainder of the valve gear operates normally.
Another object of the present invention is to provide a simple means for rendering selected valves operative or inoperative on demand, i.e., complete activation or deactivation.
A further object of the invention is to provide a method or system for improving the performance of multi-valve engines by timing one set of valves (i.e. one intake valve and one exhaust valve) being for normal operation with the other valve or set of valves (i.e. another intake valve or another pair of intake and exhaust valves) timed for maximum performance, acceleration and high speed and power, the first set of valves remaining in operation at all times and the second set of valves being activated and operating on demand for speed and acceleration.
Another object of the invention is to provide an electro-rheological valve control means which also serves to provide engine compression braking by use of the usual exhaust cam to open the exhaust valve at a predetermined time near the end of the piston exhaust stroke or at a time determined by the on-board computer microprocessor, and as a consequence, to absorb energy during compression and to dissipate it by releasing it into the exhaust system to provide a braking action.
A further object of the invention is to provide an electro-rheological valve lift mechanism which is self-contained and can easily be removed and replaced as a single unit.
A further object of the present invention is to provide an electro-rheological valve control mechanism which can be utilized in conjunction with conventional hydraulic valve lifters.
A still further object of the present invention is to provide an electro-rheological control apparatus which can be utilized on the cam and cam shaft.